What is Extended Grapheme Clusters in SWIFT?

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asked Mar 3, 2015 in Swift by john (4,220 points)
Hi All

  What is Extended Grapheme Clusters in SWIFT?

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answered Mar 3, 2015 by kalpana (3,995 points)

Hi Jhon

Every instance of Swift’s Character type represents a single extended grapheme cluster. An extended grapheme cluster is a sequence of one or more Unicode scalars that (when combined) produce a single human-readable character.

Here’s an example. The letter é can be represented as the single Unicode scalar é (LATIN SMALL LETTER E WITH ACUTE, or U+00E9). However, the same letter can also be represented as a pair of scalars—a standard letter e (LATIN SMALL LETTER E, or U+0065), followed by the COMBINING ACUTE ACCENT scalar (U+0301). The COMBINING ACUTE ACCENT scalar is graphically applied to the scalar that precedes it, turning an e into an éwhen it is rendered by a Unicode-aware text-rendering system.

In both cases, the letter é is represented as a single Swift Character value that represents an extended grapheme cluster. In the first case, the cluster contains a single scalar; in the second case, it is a cluster of two scalars:

  • let eAcute: Character = "\u{E9}" // é
  • let combinedEAcute: Character = "\u{65}\u{301}" // e followed by ́
  • // eAcute is é, combinedEAcute is é

Extended grapheme clusters are a flexible way to represent many complex script characters as a single Character value. For example, Hangul syllables from the Korean alphabet can be represented as either a precomposed or decomposed sequence. Both of these representations qualify as a single Character value in Swift:

  • let precomposed: Character = "\u{D55C}" // 한
  • let decomposed: Character = "\u{1112}\u{1161}\u{11AB}" // ᄒ, ᅡ, ᆫ
  • // precomposed is 한, decomposed is 한
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